1. Field of the Invention
This invention relates to the production of semiconductor wafers and, more particularly, to a method and apparatus for adhering an adhesive-backed tape or sheet to a semiconductor wafer.
2. Description of the Related Art
In the production of semiconductor devices, such as integrated circuits (IC), large scale integrated circuits (LSI), and very large scale integrated circuits (VLSI), a disk-like semiconductor wafer is formed with a number of electrical patterns on the surface thereof and then cut into a predetermined number of squares to obtain semiconductor chips for individual devices. Before cutting the wafer, an adhesive-backed tape or sheet is adhered to the back surface of the wafer to prevent cut chips from scattering into individual pieces.
A method for adhering a tape to a wafer is known in the prior art, in which a semiconductor wafer is placed on a supporting table and an adhesive-backed sheet, made of, for example, vinyl chloride tape, is then brought into contact with the wafer surface. Then, the entire surface of the adhesive-backed tape is rolled or brushed with a rubber roller or brush. However, there is a disadvantage with this method because the adhesive-backed sheet does not come into full contact with the wafer at the central portion thereof if the wafer is warped in such a way that the central portion thereof is concave, as shown in FIG. 11.
FIG. 10 shows a known wafer mounting apparatus for adhering an adhesive-backed sheet to a semiconductor wafer, in which reference numeral 51 denotes an upper housing; 52, a lower housing; 53, a rubber roller; 54, a motor; 55, a rail; 56, a frame; 57, an adhesive-backed sheet; and 58, a semiconductor wafer. In this known apparatus, after the pressure in the chamber is reduced by a vacuum pump (not shown) to about -750 mmHg, the single roller 53 is lowered to come into contact with the adhesive-backed sheet 57. Then, the roller 53 is moved by the motor 54 along the rail 55 to roll over the back surface of the semiconductor wafer 58 and exert a slight force to press the adhesive-backed sheet 57 against the wafer 58.
However, if the wafer 58 is warped in such a manner that the central portion is lower than the peripheral portion thereof, such as schematically and exaggeratedly shown in FIG. 11, the roller 53 comes into contact only with the peripheral portion of the wafer 58, and not with the central portion thereof. Therefore, an air cavity 60 is created between the adhesive-backed sheet 57 (under the roller 53; not shown) and the wafer 58. In this case, after the mouting of the wafer is completed, air bubbles remain at the central part 58a between the sheet 57 and the wafer 58.
In a subsequent process, the wafer 58 is cut into a number of semiconductor chips. However, if there are air bubbles remaining between the sheet 57 and the wafer 58, as mentioned above, some of the cut chips at the area corresponding to that containing air bubbles are scattered, or other cut chips are damaged. Therefore, it becomes difficult to handle these cut chips.